Existing soft ice cream machines generally are complex, whose stirring device and stirring motor are remotely connected by belt-pulley-type transmission device, are arranged vertically in a housing, have relatively large volume, need to occupy relatively large space, and have relatively large weight. Due to the use of high-power motors and compressors, despite the relatively large processing capacity, the existing soft ice cream machines will have high power consumption and high price, which lead to that the production cost is largely increased and that they are not suitable for use in commercial retail sales and household where large processing capacity is not required.
Secondly, conventional belt-pulley-type transmission needs high power motors, has high power consumption, is prone to skid and wobble during operation, has high noise, and has drawbacks of being unstable during operation and high noise pollution, etc.
Besides, in the ice cream machine currently available in the market, the return mechanism of the discharge valve is usually arranged inside the front plate of the ice cream machine. Due to machining errors or assembly errors or others factors, the gaps between the bottom of the return rod and the top of the valve plug are inconsistent, therefore it is necessary to use valve plugs with different length to match in the field. During subsequent maintenance, the front plate of the ice cream machine needs to be opened in order to maintain or replace the return components, which leads to that the assembling and the maintaining are inconvenient and time-consuming and laborious, and that accuracy of the return is low and inaccurate return is prone to occur.
In addition, the stirring device of existing ice cream machine includes hollow continuous helical structure and broken helical structure. In operation, the stirring device with hollow continuous helical structure makes the paste of ice cream to sufficiently circulate, but it has drawbacks that the stirring is insufficient and the thrust force is small, which is unfavorable for extrusion and thereby affects the work efficiency of the ice cream machine. The stirring device with broken helical structure in operation has large working thrust force and can satisfy the efficiency requirements of the ice cream machine. However, because a relatively tight clearance generally exists between the outer periphery of the stirring device and the inner wall of the stirring tank, paste of ice cream will inevitably remain on the wall of the stirring tank during the stirring and conveying of the paste of ice cream by the stirring device. The residual paste will lead to frozen tank phenomenon after being frozen, thereby gradually affect the cooling efficiency of the ice cream machine and the taste of the ice cream.
Most of existing ice cream machines use inner-and-outer-helical-type evaporator, i.e. use a double cylindrical structure in which helical groove or helical element is arranged between the inner sleeve and the outer sleeve. This kind of structure has larger heat exchange area and higher cooling efficiency compared with front-tube-type or fin-type evaporator, however, because the helical element is usually solid circular spring, the contact area between the surface of the spring and the outer wall of the inner sleeve is small, and the contact area between the gaseous or liquid refrigerant passing through the spring and the paste inside the inner sleeve is limited. Therefore, there is room for further increasing the heat exchange area to increase the cooling efficiency by improving the helical element.